1. Field of the Invention
The present invention relates to a solar battery cell, a solar battery module and a method of making solar battery module.
2. Related Background Art
In recent years, much attention has been paid to solar batteries as means for solving increasingly serious global warming and fossil energy depletion problems. A solar battery is normally formed by connecting a plurality of solar battery cells together in series or parallel. The solar battery cell includes a plurality of linear electrodes (finger electrodes) arranged in parallel on a front surface (light receiving surface) thereof and formed of Ag in order to provide power. A back surface electrode formed of Al is formed all over a back surface of the solar battery cell. Then, adjacent solar battery cells are connected together by connecting a metal wiring member (TAB wire) to the light receiving surface of one of the adjacent solar battery cells so that the metal wiring member crosses the all the finger electrodes and further connecting the TAB wire to the back surface electrode of the other solar battery cell.
Solder exhibiting proper conductivity is conventionally used to connect the TAB wire (Japanese Patent Laid-Open No. 2002-263880). Furthermore, in some cases, Sn—Ag—Cu solder, which contains no Pb, has recently been used with environmental problems taken into account (Japanese Patent Laid-Open Nos. 2002-263880 and 2004-204256). However, when these solders are used to connect the TAB wire, the solar battery cells are heated at about 220° C. or higher. Thus, the yield of the connection step may decrease or the solar battery cells may be warped. To suppress this, silicon in the solar battery cells may be increased in thickness. However, in this case, manufacturing costs increase.
Furthermore, when such solder as described is used to connect the TAB wire, the following measure needs to be taken in order to ensure wettability of the solder: electrodes (bus bar electrodes) formed of Ag is preformed on the front and back surfaces of the solar battery cell at the positions where the TAB wires are located. However, Ag is expensive, thus contributing to increasing costs. Additionally, Ag offers high electric resistance, and thin bus bar electrodes thus offer high sheet resistance. This increases power loss, thereby reducing the power generation performance of the solar battery cells. Thus, to suppress the sheet resistance of the bus bar electrodes, the bus bar electrodes need to be increased in width to some degree. This further increases the manufacturing costs.
Hence, in recent years, a method has been proposed in which a conductive adhesive with a conductive adhesion layer is used instead of the solder to connect the TAB wire (Japanese Patent Laid-Open Nos. 8-330615, 2003-133570, 2005-243935, and 2007-265635). The conductive adhesive is a thermosetting resin in which metal particles such as Al particles are mixed and dispersed. The metal particles are sandwiched between the TAB wire and the electrode of the solar battery cell to achieve electric connection. If the conductive adhesive is used to connect the TAB wire, the connection can be carried out at 200° C. or lower. This suppresses a decrease in the yield of the connection step and the warpage of the solar battery cells. Furthermore, if the conductive adhesive is used to connect the TAB wire, the wettability need not be ensured. This in turn eliminates the need for the bus bar electrodes, formed to ensure the wettability, thus reducing the use of Ag.
However, avoidance of formation of bus bar electrodes on the front or back surface of the solar battery cell prevents identification of the position where the TAB wires are connected. This may preclude the TAB wires from being accurately stuck to intended positions. When the TAB wires fail to be stuck to the intended positions, the lines of the solar battery cells may meander. Then, a residual stress may be generated in the solar battery cells, and the manufacturing yield may decrease. In this case, additional alignment marks for alignment may be formed at the intended adhesion positions. However, a complicated step of forming alignment marks increases the manufacturing costs.
The present invention has been made to solve the above-described problems. An object of the present invention is to provide a solar battery cell that enables the TAB wire to be accurately connected to the intended position, while allowing a possible increase in manufacturing costs to be suppressed.